The present invention relates to a pin sharing device and a method thereof, and more particularly, to a pin sharing device and method for a Universal Asynchronous Receiver/Transmitter (UART) module and a Universal Serial Bus (USB) module.
Integrated circuits (ICs) are used in almost all electronic equipments today. With development of the IC manufacturing process, size of an IC chip can be smaller for realizing cost reduction. At the same time, more and more functions are implemented in a single IC chip which requires more input/output (I/O) pins on the IC. The number of I/O pin counts becomes the design limit for reducing the size of the IC chip. Therefore, it is a challenge for an IC designer to properly assign each input and output pin to minimize the number of pins.
Generally, a baseband IC in a mobile phone includes a UART module and a USB module for data transmission between the mobile phone and a peripheral device or a host computer. Please refer to FIG. 1, which is a schematic diagram of a UART module 102 and a USB module 104 in a baseband IC 10. Except power and ground ports, the UART module 102 includes ports UTXD, URXD, UCTS and URTS. UTXD and URXD are used for data transmission, whereas UCTS and URTS are used for signaling control, which are not shown in FIG. 1. The USB module 104 includes two ports DP and DM both for data and command transmission. As shown in FIG. 1, transmission ports for the UART module 102 and the USB module 104 are independent, and thereby the baseband IC 10 has to provide four I/O pins for UTXD, URXD, DP and DM, which is not efficient for the limited number of pins.
On the other hand, due to the small size of the mobile phone, most of the mobile phones only have one connector so the UART function and the USB function will not be activated at the same time. Therefore, a system designer may use an analog switch for selecting the UART ports (UTXD and URXD) or the USB ports (DP and DM) to connect to the connector, which helps the UART module and the USB module share common pins on the connector. However, the analog switch results in signal distortion easily for USB 2.0 high speed transmission.